Oxidation-resistant hard composition



Patented Oct. 6, 1953 OXIDATION-RESISTANT HARD COIWPOSITION John W. Graham, Ligonier, Pa... assignor to Kennamctal Inc., Latrobe, Pa., a corporation of Pennsylvania No Drawing. Application June 28, 1951, Serial No. 234,165

14 Claims. 1

My invention relates to an improved oxidationresistant hard composition and has to do, more particularly, with a hard composition of matter which is relatively light but strong and which has high resistance to oxidation at elevated temperatures.

The principal object of my invention is to provide an improved composition of matter having a specific gravity between 5 and 7, a transverse rupture strength exceeding 90,000 pounds per square inch and which is highly resistant to oxidation or corrosion at temperatures exceeding 1500 F.

Sintered hard compositions of matter have been proposed, and have proven highly successful, which consist substantially of titanium carbide and a small percentage of columbium carbide and/or tantalum carbide, or both, sintered with a metal of the iron group as a binder metal. It

has also been proposed to make a hard composition of matter consisting of titanium carbide sintered with iron, cobalt or nickel as the binder metal, but such compositions lacked the resistance to oxidation, at temperatures exceeding 1500 R, which is requisite for the uses for which such compositions are intended.

A further object of my invention is to provide a novel hard composition of matter having suflicient strength, and high resistance to oxidation at temperatures exceeding 1500 F., which does :1

not require the use of relatively scarce and critical metals such as cobalt, nickel, columbium or tantalum.

A further object of my invention is to provide a novel hard composition of matter including titanium carbide. and iron as a part of the binder, but which has a high resistance to corrosion at elevated temperatures, such as was not obtainable when iron alone was used as the binder.

I have found that, when a hard composition 1 of matter is made by sintering titanium carbide with a binder consisting of one or more metals of the iron group, plus a certain percentage of silicon. the resultant composition is relatively light, having a specific gravity between 5 and '7,

pressed, I believe this action is due to the fact that the presence in the composition of a metal of the iron group, silicon and titanium forms a glaze or thin oxidized surface film which resists further oxidation and permeation or penetration of oxidation into the interior of the piece.

In general, my invention consists of a sintered hard composition of matter consisting substantially of titanium carbide and a binder composed of one or more metals of the iron group and silicon. I have found that the silicon should constitute from 2% to 10% by weight of the binder and that it should exceed 1% by weight of the entire composition. The binder metal employed with silicon may be iron, nickel or cobalt although I prefer to use iron, because of the present scarcity of nickel and cobalt.

I prefer to use, in making these compositions. a, titanium carbide (TiC') that is substantially devoid of free carbon, oxides and nitrides and preferably a titanium carbide prepared by the method described and claimed in United States Letters Patent of Philip M. McKenna, No.

Example 1 A mixture of 80% by weight titanium carbide (T10), 18% iron (Fe) and 2% silicon (Si) was formed into a compact oi the desired shape, which was presintered at a temperature of about 1900 F. and then subjected to final sintering at a temperature of 2600 F. The finished composition had a hardness on the Rockwell A scale of 90.2, a transverse rupture strength of 110,000 p. s. i. and a specific gravity of 5.3. A specimen of this composition was subjected to prolonged exposure at a temperature of 1800 F. for a period of 72 hours and, at the end of that time, the total increase in thickness on one face was only .0025 inch which is an indication of extremely high resistance to oxidation at high temperatures. The increase in thickness of a specimen after prolonged exposure to the'high temperature is considered a measure of its resistance to oxidation. Example 2 A mixture consisting of 80% titanium carbide presintered at a temperature of 1900 F. and then subjected to a final sintering at 2720 F. A

specimen of the composition thus made had a Rockwell A hardness of 92.5, a transverse rupture strength of 69,000 p. s. i. and a specific gravity of 5.42. The transverse rupture strength of this specimen was lower than is desirable. A specimen of this composition was subjected to a temperature of 1800" F. for 72 hours, at the end of which time the increase in thickness per face of the specimen was .0081 inch, which indicates that it was not as good in resistanc to oxidation as the specimen of Example 1 and this may be due to the fact that the amount of silicon in the binder was only 1%.

Example 3 A mixture consisting of 70% titanium carbide ('IiC), 28% iron (Fe) and 2% silicon (Si) was formed into a compact which was presintered at a temperature of 1900 F. and then subjected to final sintering at a temperature of 2720 F. A specimen of the composition thus made had a hardness on the Rockwell A scale of 88.9, a transverse rupture strength of 111,000 p. s. i. and a specific gravity of 5.64. A specimen of this composition was subjected to exposure to a temperature oi 1800 F. for 72 hours at the end of which time the total increase in thickness per face of the specimen was .0035 inch. This indicates that this third composition was very good insofar as its resistance to oxidation at high temperatures is concerned, and it also had a high transverse rupture strength.

Example 4 A powder mixture consisting of 80% titanium carbide (TiC), 18.4% iron (Fe) and 1.6% silicon (Si) was formed into a compact, which was presintered at a temperature of 1900 F. and then subjected to final sintering at 2600 F. A specimen of the composition thus made had a hardness on the Rockwell A scale of 92.0, a transverse rupture strength of 110,000 p. s. i. and a specific gravity of 5.79. A specimen of the composition was subjected to a temperature of 1800 F. for '72 hours with a total increase in thickness per face of the specimen of .0016 inch. This indicates an extremely good resistance to oxiable transverse rupture strength.

Example 5 A powder mixture was made up consisting of 80% titanium carbide (TiC), 18.5% nickel (Ni) and 1.5% silicon (Si). A compact made from this powder mixture was presintered at a temperature of 1900 F. and subiected to final sintering at a temperature of 2600 F. A specimen of the composition so made had a hardness on the Rockwell A scale of 89.8. a transverse rupture stren th of 155,000 p. s. i. and a specific gravity of 5.19. A specimen of this composition was subjected to exposure to a temperature of 18000 F. for a period of '72 hours, at the end of which time the total increase in thickness per face of the specimen was .0042 inch. It is to be noted that this specimen had a hi h transverse rupture strength compared with the Others but the resistance to oxidation was not as good as some of the others, although it was high enough to be of value.

Example 6 A powder mixture consisting of titanium carbide (TiC), 18.5% cobalt (Co) and 1.5% silicon (Si) was formed into a compact which was sintered, without presintering, at a temperature of 2800 F. A specimen of the composition so made had a hardness on the Rockwell A scale of 89.8, a transverse rupture strength of 108,000 p. s. i. and a specific gravity of 5.33. A specimen of this material has not been tested for resistance to oxidation at high temperatures but there is reason to believe that it will prove equally resistant to oxidation, when subjected to temperatures exceeding 1500 F. for long periods.

As a result of the tests that I have made, I believe that silicon should be present to an amount in excess of 1% by weight of the entire composition. If silicon is present to a less amount it does not seem to be eifective to increase the resistance of the composition against oxidation at.

high temperatures. On the other hand, I have found that too much silicon is detrimental due to the fact that the excess of silicon causes theiormation, with the iron, cobalt or nickel, of a eutectic having a melting point below 2300" R, which is undesirable in the manufacture of sintered hard compositions of matter for use at high temperatures. I believe, therefore, that the silicon should not constitute more than about 10% of the total weight of the binder.

The compositions including iron, as the main ingredient of the binder, are particularly interesting because nickel and cobalt are at present relatively scarce and critical materials, while iron is not. While a composition made up of titanium carbide and iron as a binder would have sufilcient strength, it would not be at all resistant to oxidation at high temperatures and therefore would not be at all useful for application in situations where the part is to be exposed for long periods to temperatures exceeding 1500 F. I have found, however, that the addition of silicon, constituting from 2% to 10% of the binder, not only gives a composition which has the requisite strength but also one that is extremely resistant to oxidation at the high temperatures to which such materials may be subjected. There is the added advantage that each of the ingredients used in these compositions are readily available and by no means scarce.

I am aware that the hard compositions of matter disclosed herein may be varied considv erably without departing from the spirit of my invention and, therefore, I claim my invention broadly as indicated by the appended claims.

Having thus described my invention, what I claim as new and useful and desire to secure by Letters Patent is:

1. A sintered hard composition of matter characterized by such high resistance to oxidation at high temperatures that the total increase in thickness on one face oi! a specimen after exposure at a temperature of 1800" F. for a period oi '72 hours does not exceed .005 inch consisting essentially of titanium carbide and a binder consisting of silicon and at least one metal from the group consisting of iron, cobalt and nickel, the

silicon constituting at least 1.5% of the composition and from 6.6% to 10% of the binder.

2. The composition of claim 1 in which the the binder is composed of iron and silicon.

3. The composition of claim 2 in which the silicon constitutes about 6.87% 01 the binder and the binder constitutes about 30% of the composition.

4. The composition of claim 1 in which the binder is composed of nickel and silicon.

5. The composition of claim 4 in which the silicon constitutes about 7.5% o! the binder and the binder constitutes about 20% of the composition.

6. The composition 01' claim 1 in which the binder is composed of cobalt and silicon. V

7. The composition of claim 6 in which the silicon constitutes about 7.5% of the binder and .the binder constitutes about 20% of the composition.

8. A hard composition oi matter characterized by such high resistance to oxidation at high temperatures that the total increase in thickness on one face or a specimen after exposure at a temperature of 1800 I". for a period of 72 hours does not exceed .005 inch, a transverse rupture strength exceeding 90,000 p. s .i., and a specitlc gravity between 5 and 7, consisting essentially of titanium carbide (TiC), substantially devoid of free carbon, oxides and nitrides, sintered with a binder consisting oi silicon and at least one metal from the group consisting of iron, cobalt and silicon constitutes about 7.5% of the binder and the binder constitutes about 20% of the composition.

13. The composition of claim 8 in which the binder is composed of cobalt and silicon.

14. The composition of claim 13 in which the silicon constitutes about 7.5% or the binder and the binder constitutes about 20% of the composition.

JOHN w. GRAHAM.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Schwarzkopf June 17, 1947 Number 

1. A SINTERED HARD COMPOSITION OF MATTER CHARACTERIZED BY SUCH HIGH RESISTANCE TO OXIDATION AT HIGH TEMPERATURES THAT THE TOTAL INCREASE IN THICKNESS ON ONE FACE OF A SPECIMEN AFTER EXPOSURE AT A TEMPERATURE OF 1800* F. FOR A PERIOD OF 72 HOURS DOES NOT EXCEED .005 INCH CONSISTING ESSENTIALLY OF TITANIUM CARBIDE AND A BINDER CONSISTING OF SILICON AND AT LEAST ONE METAL FROM THE GROUP CONSISTING OF IRON, COBALT AND NICKEL, THE SILICON CONSTITUTING AT LEAST 1.5% OF THE COMPOSITION AND FROM 6.6% TO 10% OF THE BINDER. 